The present invention relates to a thermal barrier coating applied to the surface of a superalloy article (e.g., a gas turbine engine turbine blade, and to a method of applying the thermal barrier coating).
The constant demand for increased operating temperature in gas turbine engines was initially met by air cooling of the turbine blades and the development of superalloys from which to manufacture the turbine blades and turbine vanes, both of which extended their service lives. Further temperature increases necessitated the development of ceramic coating materials with which to insulate the turbine blades and turbine vanes from the heat contained in the gases discharged from the combustion chambers, again the operating lives of the turbine blades and turbine vanes was extended. However, the amount of life extension was limited because the ceramic coatings suffered from inadequate adhesion to the superalloy substrate. One reason for this is the disparity of coefficients of thermal expansion between the superalloy substrate and the ceramic coating. Coating adhesion was improved by the development of various types of aluminum containing alloy bond coatings which were thermally sprayed or otherwise applied to the superalloy substrate before the application of the ceramic coating. Such bond coatings are typically of the so-called aluminide (diffusion) or xe2x80x9cMCrAlYxe2x80x9d types, where M signifies one or more of cobalt, iron and nickel.
Use of bond coatings has been successful in preventing extensive spallation of thermal barrier coatings during service, but localized spallation of the ceramic coating still occurs where the adhesion fails between the bond coating and the ceramic coating. This exposes the bond coating to the full heat of the combustion gases, leading to premature failure of the turbine blade or turbine vane.
The present invention seeks to provide a novel bond coating for a thermal barrier coating which is less prone to localized failure and more suitable for long term adhesion to a superalloy substrate.
The present invention seeks to provide a method of applying a thermal barrier coating to a superalloy substrate so as to achieve improved adhesion thereto.
According the present invention provides a multi-layer thermal barrier coating for a superalloy substrate, comprising a bond coating, an oxide layer on the bond coating and a ceramic thermal barrier coating on the oxide layer, the bond coating containing aluminum at least in the outer region of the bond coating, the bond coating containing at least one metal compound at least in the inner region of the bond coating, the at least one metal compound is selected such that at least one harmful element diffusing from the superalloy substrate into the aluminum containing alloy bond coating substrate reacts with the metal compound to release the metal into the bond coating and to form a compound with the harmful element.
It is believed that the metal compound in the bond coating reduces the movement of damaging elements from the superalloy substrate to the oxide layer. It is believed that the damaging elements diffusing from the superalloy substrate react with the metal compound such that an exchange reaction occurs and the damaging elements form benign compounds and the metal is released into the bond coating.
The at least one metal compound may be a carbide, an oxide, a nitride or a boride.
For example the at least one metal compound may be one or more of chromium carbide, manganese carbide, molybdenum carbide, aluminum carbide, nickel carbide or tungsten carbide.
The at least one metal compound may be in the form of particles distributed evenly at least throughout the inner region of the bond coating.
The bond coating may comprise an aluminum containing alloy bond coating with the at least one metal compound distributed evenly throughout the whole of the aluminum containing alloy bond coating. The aluminum containing alloy bond coating may comprise a MCrAlY alloy, where M is at least one of Ni, Co and Fe.
The bond coating may comprise a first coating and a second aluminum containing alloy coating on the first coating, the first coating comprising a nickel aluminum alloy, a nickel cobalt alloy, a nickel chromium alloy, a cobalt aluminum alloy or a cobalt chromium alloy with the at least one metal compound distributed evenly throughout the whole of the first coating.
The bond coating may comprise a first coating and a second aluminum containing alloy coating on the first coating, a platinum-group metal enriched aluminum containing alloy layer on the aluminum containing alloy coating, a coating of at least one aluminide of the platinum-group metals on the platinum-group metal enriched aluminum containing alloy layer, the first coating comprising a nickel aluminum alloy, a nickel cobalt alloy, a nickel chromium alloy, a cobalt aluminum alloy or a cobalt chromium alloy with the at least one metal compound distributed evenly throughout the whole of the first coating.
The bond coating may comprise an aluminum containing alloy bond coating, a platinum-group metal enriched aluminum containing alloy layer on the aluminum containing alloy coating, a coating of at least one aluminide of the platinum-group metals on the platinum-group metal enriched aluminum containing alloy layer, the at least one metal compound being distributed evenly throughout the whole of the aluminum containing alloy bond coating. The aluminum containing alloy bond coating may comprise a MCrAlY alloy, where M is at least one of Ni, Co and Fe.
The present invention also provides a method of applying a multi-layer thermal barrier coating to a superalloy substrate comprising the steps of: applying an aluminum containing alloy bond coating to the superalloy substrate, the aluminum containing alloy bond coating including at least one metal compound distributed evenly throughout the whole of the aluminum containing alloy bond coating, the at least one metal compound is selected such that at least one harmful element diffusing from the superalloy substrate into the aluminum containing alloy bond coating reacts with the metal compound to release the metal into the bond coating and to form a compound with the harmful element, forming an oxide layer on the aluminum containing alloy bond coating and applying a ceramic thermal barrier coating on the oxide layer.
The present invention also provides a method of applying a multi-layer thermal barrier coating to a superalloy substrate comprising the steps of: applying a first coating to the superalloy substrate, the first coating including at least one metal compound distributed evenly throughout the whole of the first coating, the at least one metal compound is selected such that at least one harmful element diffusing from the superalloy substrate into the first coating reacts with the metal compound to release the metal into the first coating and to form a compound with the harmful element, applying a second aluminum containing alloy coating on the first coating, forming an oxide layer on the aluminum containing alloy bond coating and applying a ceramic thermal barrier coating on the oxide layer.
The present invention also provides a method of applying a multi-layer thermal barrier coating to a superalloy substrate comprising the steps of: applying a a first coating to the superalloy substrate, the first coating including at least one metal compound distributed evenly throughout the whole of the first coating, the at least one metal compound is selected such that at least one harmful element diffusing from the superalloy substrate into the first coating reacts with the metal compound to release the metal into the first coating and to form a compound with the harmful element, applying a second aluminum containing alloy coating on the first coating, applying a layer of platinum-group metal to the aluminum containing alloy coating, heat treating the superalloy substrate to diffuse the platinum-group metal into the aluminum containing alloy coating to create a platinum-group metal enriched aluminum containing layer and a coating of at least one aluminide of the platinum-group metals on the platinum-group metal enriched aluminum containing alloy layer, forming an oxide layer on the coating of at least one aluminide of the platinum-group metals and applying a ceramic thermal barrier coating to the oxide layer.
The present invention also provides a method of applying a multi-layer thermal barrier coating to a superalloy substrate comprising the steps of: applying an aluminum containing alloy bond coating to the superalloy substrate, the aluminum containing alloy coating including at least one metal compound distributed evenly throughout the whole of the aluminum containing alloy coating, the at least one metal compound is selected such that at least one harmful element diffusing from the superalloy substrate into the aluminum containing alloy coating reacts with the metal compound to release the metal into the aluminum containing alloy coating and to form a compound with the harmful element, applying a layer of platinum-group metal to the aluminum containing alloy coating, heat treating the superalloy substrate to diffuse the platinum-group metal into the aluminum containing alloy coating to create a platinum-group metal enriched aluminum containing alloy layer on the aluminum containing alloy coating and a coating of at least one aluminide of the platinum-group metals on the platinum-group metal enriched aluminum containing alloy layer, forming an oxide layer on the coating of at least one aluminide of the platinum-group metals and applying a ceramic thermal barrier coating to the oxide layer.
The at least one metal compound may be a carbide, an oxide, a nitride or a boride.
For example, the at least one metal compound may be one or more of chromium carbide, manganese carbide, molybdenum carbide, aluminum carbide, nickel carbide or tungsten carbide.
The at least one metal compound may be in the form of particles distributed evenly throughout the first coating of the bond coating or throughout the aluminum containing alloy coating. The aluminum containing alloy bond coating may comprise a MCrAlY alloy, where M is at least one of Ni, Co and Fe.
The first coating may comprise a nickel aluminum alloy, a nickel cobalt alloy, a nickel chromium alloy, a cobalt aluminum alloy or a cobalt chromium alloy with the at least one metal compound distributed evenly throughout the whole of the first coating.